The oligomerization of olefins such as isobutylene using a sulfonic acid-type ion exchange resin catalyst is well-known in the art. For instance, U.S. Pat. No. 4,100,220 describes isobutylene oligomerization using a sulfonic acid resin catalyst and tertiary butyl alcohol selectivity enhancing modifier. In addition, U.S. Pat. No. 4,447,668 discloses isobutylene oligomerization using sulfonic acid resin catalyst A-15 with methyl t-butyl ether as solvent. Further, U.S. Pat. No. 5,877,372 describes the selective oligomerization of isobutylene using a sulfonic acid resin catalyst, tertiary butyl alcohol selectivity enhancing modifier and isooctane diluent. Lastly, U.S. Pat. No. 6,376,731 discloses the oligomerization of isobutylene in the presence of a C3-C4 alkane diluent to enhance oligomerization selectivity and tertiary butyl alcohol to promote selectivity to diisobutylene.
The diisobutylene product may be used as such or may be hydrogenated to isooctane as described in U.S. Pat. Nos. 5,877,372 and 6,376,731. Diisobutylene and isooctane are potential fuel blending compositions.
Sulfonic acid ion exchange resins for isobutylene oligomerization are typically supplied as water wet resins containing greater than 50 wt. % water. Unfortunately, the presence of water hinders the oligomerization reaction. In order for the sulfonic acid resin to be active in isobutylene oligomerization, the sulfonic acid resin must be dried. Typically, the resin is dried by vacuum or by heat to remove the water from the resin or the resin may be contacted with a solvent to remove the water from the resin. The solvent contact is performed using an organic liquid or reactant feed and is performed under ambient conditions. The vacuum or heat drying method adds unwanted cost to the process and the solvent contact method requires an inordinate amount of time to dry the resin.
In sum, new methods to produce diisobutylene by oligomerization of isobutylene over a sulfonic acid-type ion exchange resin catalyst are needed. Particularly needed are processes for drying the sulfonic acid resin catalyst prior to the oligomerization step.